Catalytic conversion of ligno-cellulosic biomass into fuels and chemicals

ABSTRACT

The invention provides a process for producing ethyl esters and hydrocarbons from lignocellulosic biomass materials. The process comprises two steps: the first step being an acid ethanolysis (solvolysis with ethanol) of the biomass in oxidizing medium; the second step being the catalytic conversion of the by-product diethyl ether and, optionally, light ethyl esters, into hydrocarbons over ZSM-5 zeolite catalyst. Cellulose, hemicellulose and part of the lignin are converted in the first step. The oxidizer used in this first conversion step is preferably and most preferably hydrogen peroxide activated by Fe (II) (Fenton-type reagent), and/or Ti (IV) ions. The final products may include ethyl levulinate (diesel-grade additive), light ethyl esters (ethyl formate and ethyl acetate), levulinic acid, succinic acid, methanol, gasoline-range hydrocarbons and C 2 -C 4  hydrocarbons.

FIELD OF THE INVENTION

This invention relates to a process for producing ethyl esters andhydrocarbons from ligno-cellulosic biomass materials.

BACKGROUND OF THE INVENTION

Ligno-cellulosic biomass material designates materials such as wood,forestry, paper-making or cardboard-making residues, agriculturalresidues, municipal wastes and perennial grasses. Paper pulp used in thepulp and paper industry is an example of cellulosic material albeit poorin lignin content. Other examples of ligno-cellulosic biomass materialsare: wood chips (jack pine, spruce, etc), switch grass or loggingoperation residues. Ligno-cellulosic biomass material will vary in theircomposition in cellulose, hemicellulose, lignin and other species.Typically, ligno-cellulosic materials contain as main components:cellulose (about 35-50 wt %), hemicellulose (about 23-30 wt %) andlignin (about 15-32 wt %).

Cellulose is made up of crystalline bundles of polysaccharides thatconsist of thousands of linked glucose molecules. Chains of sugarmolecules are also found in hemicellulose, it is however an amorphoussubstance. More particularly, hemicellulose consists of a randomcombination of various carbohydrate molecules such as xylose, mannoseand arabinose. Lignin, a macromolecule of substituted phenols, bindstogether the other components.

There are known ways of converting cellulose and hemicellulose intofuels and chemicals. The most common technique is to submit these tohydrolysis (using acid catalysts or enzymes) breaking these into theirconstituent sugars: the resulting molecules (mainly glucose) arefermented in ethanol (or other chemical intermediates) in the presenceof yeasts. For example, bioethanol is currently produced by enzymaticfermentation of sugars from various biomass sources such as corn-grain(U.S.A.) or sugar cane (Brazil).

Lignin is much more difficult to depolymerize or decompose into itsconstituents. It is only possible to decompose lignin in quite harsh andhydrogenating conditions because of known its high oxygen content andthe dominance of aromatic structures.

In recent years, environmental and social considerations have led to theuse of new raw materials. In fact, all around the world, it is stressedthat new biomass conversion technologies must not compete with foodproduction, as first-generation biofuels do. Biodiesel, for example, iscurrently derived from rapeseed (canola) or soya bean oil whilebioethanol is currently produced from plant matter containing starch orsugar. These processes compete with the use of these materials assources of food.

Second-generation biofuels and biochemicals (those that do not directlycompete with use as food), are derived from cellulose-hemicellulosebased matter. Levulinic acid (reference 1), formic acid and their alkylesters (ex. ethyl levulinate and ethyl formate, respectively) belong tosuch category of bio-fuels and biochemicals. In contrast, more advancedgeneration biofuels like those of the present invention are derived fromall the three main components of the biomass, e.g. including lignin.

Production of Alkyl Levulinates and Light Alkyl Esters

The catalytic conversion of cellulose and hemicellulose into alkyllevulinates and light alkyl esters is known to be carried out in a) asingle step process or b) a two-step process.

In a single step process, alcohol is used as a reactant and solvent. Atleast one acidic catalyst is used, typically a mineral acid diluted inthe alcohol. The final products of the reaction consist mainly of alkyllevulinate (main product), levulinic acid, alkyl formate, 2-furfural(2-furfuraldehyde), alkyl acetate and solid “residues”. The use ofalcohol allows the occurrence of two chemical reactions: alcoholysis andesterification. However, the by-product dialkyl ether is also produceddirectly from the alcohol in quite significant amounts, the amountsvarying with process conditions such as temperature. If the alcohol isethanol, this ether is diethyl ether (ethyl ether). Diethyl ether can beconsidered, because of its high volatility at room temperature, as aninconvenience for various operations (handling, storage). Solid residues(commonly called lignin char) are also produced in a significantquantity.

It is to note that lignin char is a complex mixture of solid polymericand resinous products formed by side-conversion(degradation-condensation) of various reaction intermediates fromcellulose and hemicellulose. Lignin char that is present in the finalsuspension in both dissolved and (mainly) solid forms includes also theunconverted lignin (most of the time, seriously degraded).

In a two-step process, both catalytic steps involve acidic catalysts.The first step is the hydrolysis of cellulose and hemicellulose: thisreaction produces levulinic acid and some by-products such as formicacid and 2-furfural. The second step is the esterification of theresulting acids, producing the corresponding alkyl esters. It is to notethat, in some harsh conditions, 2-furfural resulting from the acidcatalyzed degradation of the reaction intermediates of hemicelluloses,is converted into formic acid.

It is also noted that in the step of hydrolysis of cellulose andhemicellulose of the lignocellulosic material, there is a complexsequence of thermochemical and catalytic events: aperture of thelignocellulosic biomass structure, exposure of the cellulose andhemicellulose components, catalytic decrystallization/depolymerisationof cellulose and catalytic depolymerisation of the amorphoushemicellulose into respective sugar molecules, and finally,dehydration-decomposition of the latter into levulinic acid and formicacid, and 2-furfural, respectively. All these physico-chemical changesoccur in the presence of a diluted solution of mineral acid and atmoderately elevated temperatures. Usually, once the hydrolysis iscompleted, it is necessary to extract the produced levulinic acid fromthe lignin chars by various extractive techniques. Finally, at the endof the second step (esterification), ethyl levulinate has to beseparated from other by-products.

Extraction-Separation of the Final Products

In the prior art, several problems arise with the extraction and thenthe separation of the products being produced in the reaction phase.

The important mass of solid residues (tars or lignin char) that usuallyact as a sponge for the liquid products, needs to be separated usingfiltration, centrifugation, etc. These techniques normally lead toimportant losses of products and can be energy consuming withoutresulting in sufficiently char-free liquid mixtures (of products)because some char are still dissolved in these aqueous or alcoholicmixtures.

Distillation (fractional distillation), vacuum-distillation,evaporating-stripping, solvent extraction, etc., areseparation-purification techniques that are quite demanding in energy,and/or that can make use of harmful solvents.

Therefore, the contribution to the production cost of these conventionaltechniques of products extraction-separation can be enormous (typicallylarger than 60%).

Recently, a fully integrated apparatus has been developed that allowsproduction of alkyl levulinates and related liquid products fromcellulosic biomass and to carry out the extraction-separation of theseproducts by using appropriate procedures. This one-pot system, describedin reference 2 (R. Le Van Mao, Q. Zhao, G. Dima and D. Petraccone,Catalysis Letters (2011) 141: 271-276), consists of a batch reactorconnected to a system of condensers, that are in turn connected to adry-vacuum system (DVS). The latter device can deliver a mild vacuum upto a maximum of 3-5 torr (see FIG. 1 of reference 2). No environmentallyharmful solvent is used and the obtained liquid fraction can be directlyblended after drying into gasoline or diesel/biodiesel. The entiresystem used for the extraction-separation of the final products is namedMVAD or mild vacuum-assisted distillation.

With such experimental set-up, it is possible to carry out theconversion of cellulosic biomass into alkyl levulinates and relatedliquid products by two alternative procedures (reference 2):

a) the direct method (D) consists of performing the conversion in acidicmedium and with ethanol that acts as co-reactant and solvent;

b) the sequential method (SEQ) consists of first carrying out the acidhydrolysis of the cellulose (and hemicellulose) of the biomass,producing levulinic acid and other carboxylic acids. Water of thereaction medium is then removed by using the MVAD procedure, and isreplaced by ethanol that converts these acids into ethyl esters. In suchsequential procedure, the liquid acid catalyst is used for both steps.

The extraction-separation of the final products is the same for bothprocedures, D and SEQ.

Reference 2 reports that the yields in alkyl levulinates (particularly,ethyl levulinate) were almost the same for the two procedures. However,it was found later that the two-step procedure (SEQ) is too energyconsuming whereas the direct method (procedure D) produced diethyl ether(DEE) as a by-product (by direct dehydration of ethanol) that might besignificant at the temperatures used (180° C.-200° C.).

Production of Diethyl Ether (DEE)

DEE is the unwanted by-product because of its low boiling point (+34.5°C.), its relatively high flammability and its quite limited commercialuse (mainly as an organic solvent). Thus, limited production of DEE orits near total elimination during biomass conversion is highlyrecommended.

Raw Materials Used

Reference 2 shows that several raw biomass materials were converted tobiofuels or biochemicals, for example: wood chips (jack pine, spruce, .. . ), paper pulp, switch grass, forestry residues and municipal wastes.It is obvious that their individual composition in cellulose,hemicellulose, lignin and other species, is different in accordance withthe type of cellulosic biomass material being used. Therefore theresulting product spectrum depends on the composition of the rawmaterial used.

Lignin

In the prior art regarding the acid-treatment of biomass, lignin istypically slightly depolymerised so that cellulose and hemicellulose canbe released for further conversion to liquid biofuels or biochemicals.In the prior art, the lignin itself essentially did not convert tobiofuels or biochemicals.

References 1-7 are examples of prior art technology. The content ofwhich is herein incorporated by reference in their entirety.

SUMMARY OF THE INVENTION

The present invention relates to a method/procedure in two steps bothinvolving catalysts for conversion of ligno-cellulosic biomass intobiofuels and biochemicals.

The first step converts ligno-cellulosic biomass materials into liquidproducts and a solid residue called tars or lignin char. This consistsof submitting said materials to a cracking reaction in oxidative/acidic/ ethanol containing/ medium at moderate temperature.

The second step can essentially eliminates the unwanted by-product DEEby conversion over acidic nanocatalyst, preferably zeolite, mostpreferably ZSM-5 zeolite. Each step will be described in further detail.

In relation to the first step, the ligno-cellulosic biomass materialssuitable for use by the present invention include all biomass materialsthat contain cellulose, hemicellulose and lignin. The preferred catalystis sulphuric acid present in very dilute solution in ethanol. Thepreferred oxidizing species is hydrogen peroxide in aqueous solution.Most preferred oxidation activating species include Fe (II) preferredoxidation species include Fe (II) ions, Ti (IV) ions, H₂MoO₄ and/ormethyltrioxorhenium (VII), these species being added to the reactionmedium in very small amounts. The combination of Fe (II) ions andhydrogen peroxide is known as Fenton's reagent. By using aninorganic/organic sulphite or carbonate that can bind tofurfuraldehyde-based intermediates, thus decreasing the rate ofpolymerization of the latter species, better yields of wanted productsare obtained.

The moderate temperature is in the range of about 120° C. to about 230°C. Whenever used herein, “about” means + or −10% of the values. It isseen that a multi-heating-step procedure is preferably used to increaseproduct yields.

The main conversion products of the ligno-cellulosic biomass are liquidethyl esters such as ethyl levulinate, ethyl formate and ethyl acetate.Some by-products are also obtained (methanol, 2-furfural, succinic acid,levulinic acid), however, in smaller amounts.

The second step can essentially eliminate DEE by conversion over acidicnanocatalyst, preferably zeolite, most preferably ZSM-5 zeolite toobtain gaseous hydrocarbons and gasoline grade liquids. The DEEconversion can be carried out in a tubular reactor. The temperatureranges from about 280° C. to about 340° C. Gaseous products includeC₂-C₄ olefins, diolefins and paraffins. Liquid hydrocarbons are in thegasoline range, containing a large proportion of BTX (benzene, tolueneand xylenes) aromatics. A moderate dilution of DEE with water was seento considerably decrease the coke deposition onto the zeolite surface,thus contributing to increasing the on-stream stability of the catalyst(decreasing thus the need for frequent catalyst regeneration, i.e.decreasing the emission of greenhouse gases, carbon oxides). Finally, ifother light ethyl esters and methanol produced in the first steps arefed to the second reactor along with DEE, essentially only hydrocarbonsare obtained in corresponding yields, the various oxygenates in the feedbeing essentially converted.

BRIEF DESCRIPTION OF FIG. 1

FIG. 1 is schematic representation of a production plant based on thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of specific embodiments thereof, given by way of examples.

Conversion of Biomass into Ethyl Esters

The present invention is illustrated in further details by the followingnon-limiting examples of the production of ethyl esters and theirextraction-separation from the conversion medium.

Experimental

Referring to FIG. 1, a Parr pressure reactor (10) (Capacity=1 liter)equipped with a magnetic-driven stirrer, a water cooling system,temperature and pressure gauges, and safety devices was used for ourtesting. As reported in reference 1, this reactor was connected with aseries of condensers (14) and a dry-vacuum system (Welch, Model 2028)that could provide a mild vacuum from 1 atmosphere to 2-3 torr. Anassembly of collecting flasks and valves (not shown) allowed thecollection of liquid products during the run without disturbing thevacuum assisted distillation operation.

A gas chromatograph set (Agilent Technologies 7890 A, Network GC system)equipped with a DB-Wax capillary column (always from Agilent Tech), wasused for the analysis of the reaction products (ref. 1). 1-propanol wasused as internal standard because water was always present in the liquidproducts.

In the presence of ethanol and dilute solution of sulphuric acid, thereaction products are the following:

Ethyl levulinate (EL), levulinic acid (LA), ethyl formate (EF), ethylacetate (EA), others: 2-furfural (2-F) and eventually, methanol (MeOH).RP is the sum of all these products given by the biomass materials.

Diethyl ether (DEE) is formed directly from ethanol in presence of themineral acid and is considered a by-product.

Raw Cellulosic Materials Used

Results obtained with three biomass materials are herein reported, thatinclude:

-   -   a) Wood chips JP (jack pine of Quebec). This ligno-cellulosic        material has the following approximate composition (dried form):        cellulose=42 wt %, hemicellulose=26 wt % , lignin=31 wt % and        others=1 wt %;    -   b) Wood chips SP (spruce of Quebec). This ligno-cellulosic        material has the following approximate composition (dried form):        cellulose=40 wt %, hemicellulose=27 wt %, lignin=32 wt % and        others=1 wt %. It is to note that the chemical structures of the        hemicelluloses of the wood JP and SP are different from each        other;    -   c) Bleached paper pulp (provided by Cascades Corporation) was        used as a model of cellulosic biomass materials. This paper pulp        had high contents in cellulose and hemicellulose (78 wt % of        cellulose, 16 wt % of hemicellulose and the balance (6 wt %),        being some organic and inorganic compounds). Before the        experimentation, the paper pulp was cut in small pieces (size of        a few cm) and dried at 120° C. overnight (average moisture        content=6.7 wt %).

Coupling of Catalytic/Chemical Reactions: Use of an Acid Catalyst and aChemical Oxidizer

Example 0 (Table 1) reports the yields of products obtained by theacidic conversion of wood chips (jack pine) in ethanol medium. Example 1reports the results that were obtained with a reaction medium containingH₂O₂ (oxidizer), there are some large differences in product yields:

-   -   Ethyl levulinate is produced at significantly higher yield,    -   The yields of ethyl formate and ethyl acetate drastically        increased, suggesting a strong action of the oxidizer on        reaction intermediates, mostly on those of hemicellulose,    -   Methanol was formed in quite significant amount, suggesting that        lignin (very) partially underwent conversion in such        oxidizing-acidic medium,    -   In oxidizing conditions used in examples 1 to 6, almost no        levulinic acid was obtained, meaning that the esterification of        levulinic acid was complete. In addition, 2-furfural disappeared        almost completely from the product spectrum, suggesting that        this compound normally formed from hemicellulose was further        converted into formic acid (finally, ethyl formate by reaction        with ethanol).

TABLE 1 Effect of the oxidizer in the reaction medium and apre-treatment phase in the heating procedure on the product yields. Massof raw material: wood chips (jack pine, dried) = 80 g; 45 g of 3.0NH₂SO₄ in absolute ethanol, 210 g of absolute ethanol, 25 g of H₂O₂ (40wt %): thus, acid concentration in the liquid phase = 2.60 wt %,concentration of H₂O₂ = 3.57 wt %. Example number 0(*) 1 2 3 4 5 6 H₂O₂NO YES YES YES YES YES YES Heating steps T₁ (° C.)/time in min NO NO140/30  140/60  140/120 140/120 140/60  T₂ (° C.)/time in min 190/100157/180 157/180 157/180 157/180 157/120 153/180 Product yield (wt %)EL(**) 15.8 14.6 20.3 21.3 21.5 16.3 18.2 EF 5.4 13.1 15.7 16.0 15.015.7 15.3 EA 2.6 6.2 6.2 6.5 5.7 6.1 6.3 2-F 0.9 0.0 0.3 0.0 0.3 0.4 0.3Methanol (others) 0.0 1.5 1.4 1.2 1.3 1.4 1.4 (2.2) Total Reaction 26.935.4 43.9 45.0 43.8 39.9 41.5 products (RP) (sum of five above lines)DEE(***) as by- 64.3 46.2 47.3 47.8 47.6 44.0 41.5 product (*)Resultsreported in reference 1 in operating conditions D with no H₂O₂ inreaction medium. (**)No or very little LA (<0.1 wt %), produced.(***)DEE is the product of the direct dehydration of ethanol.

Effect of the Pre-Conditioning (Partial Delignification) Step on theProduct Yields

When a first heating step was incorporated into the conversion procedure(examples 2 to 6 of Table 1), the yields of ethyl levulinate and ethylformate dramatically increased, suggesting that the cellulose was betterexposed for conversion into esters of its levulinic and formic acids.These examples (2-6) also showed that there was a certain balancebetween the pre-conditioning phase and the main step, so that a maximumyield of products could be obtained (conditions of example 3). Tosupport the hypothesis of a low-temperature pre-conditioning phasehaving positive effect, we can evoke the boiling point of hydrogenperoxide that is 150° C.: in fact, it was suggested that the protonatedform of H₂O₂ could be a strong oxidizing agent for carbohydrates[reference 2].

Ligno-Cellulosic Versus Cellulosic Materials

In order to show the differences in the product spectrum when acellulosic material such as paper pulp was used instead of aligno-cellulosic material such as jack pine chips, paper pulp thatcontain little or no lignin was tested in the same conditions as example3 of Table 1 (wood chips).

Results of Example 7 of Table 2, when compared with those of Example 3of Table 1 shows that:

-   -   a) Paper pulp did not produce any methanol because the latter        should come from the lignin;    -   a) The production of ethyl levulinate (and also levulinic acid)        should be higher with the paper pulp because the latter raw        material contained much more cellulose than the wood chips.

Because the degree of crystallinity of cellulose in the paper pulp washigher than that of the wood chips, slightly more severe conditions ofconversion (slightly higher acid concentration and reactiontemperatures) were used with Example 8 (Table 2): effectively, theconversion to ethyl levulinate was higher suggesting that the newoperating conditions could increase the efficiency of the acid attack ofthe cellulose in the paper pulp.

On the other hand, by using a one-step conversion procedure (Example 9versus Example 8, all of Table 2), similar levels of conversion intoethyl levulinate and other esters were obtained, suggesting that thefirst conversion step may be skipped when the used cellulosic biomasslike the paper pulp did not contain lignin.

Thus, data of Tables 1 and 2 indicate that the lignin component was alsoconverted with an acidic and oxidative medium (presence of methanol,known to be produced by decomposition of lignin). However, the level ofconversion of lignin was still low.

TABLE 2 Conversion of paper pulp, an example of cellulosic material.Example number 7 8 9 Acid concentration (wt %) 2.60 2.75 2.75Concentration of H₂O₂ (wt %) 3.57 3.53 3.53 Temperature in ° C. (time inmin) Step 1 140 (60)  143 (60)  NO Step 2 157 (180) 160 (180) 163 (180)Product yields (wt %) EL + LA 23.9 30.2 31.2 EF 17.6 20.6 17.9 EA 5.25.1 4.6 2-F 1.2 0.0 0.0 Methanol 0.0 0.0 0.0 Total RP (sum of five abovelines) 47.9 55.9 53.7 DEE (by-product) 31.9 50.3 45.5

Effect of the Content of Hydrogen Peroxide

Hydrogen peroxide is a strong oxidizer for carbohydrates and theirreaction intermediates. Because the various organic acids formed aredegradation products of theses carbohydrates, hydrogen peroxide has astrong influence on the distribution of the final products. It is worthnoting that with the increased concentration of the oxidizer, the yieldsof methanol and other light ethyl ethers noticeably increase at theexpenses of ethyl levulinate.

TABLE 3 Effect of the concentration of H₂O₂ in the liquid phase. Acidconcentration = (2.60 wt %, water = 5.4 wt %, heating steps = same as inExample 3). Example number 10 (=Ex. 3) 11 12 Concentration of H₂O₂ (wt%) 3.57 5.36 1.79 EL 21.3 17.8 17.5 LA 0.0 1.1 1.0 EF 15.7 17.5 16.4 EA6.2 6.8 5.4 2-F 0.0 0.4 0.3 Methanol 1.2 1.7 1.1 Total RP (sum of fiveabove 45.0 45.3 41.7 lines) DEE (by-product) 47.8 45.5 51.0

Presence of Fe (II)—Based Catalyst in the Reaction Medium (Use ofFenton-Type Reagents)

Fe (II) ions, added to H₂O₂, is known to form the Fenton's reagent withstrong oxidizing properties for converting numerous organic compounds[reference 5]. Fenton-type reagents are usually used to degrade organiccontaminants in waters. Surprisingly, in the cellulosic biomassconversion, Fe(II) ions when incorporated into the reaction medium thatalready contains hydrogen peroxide, significantly increased the yield ofall ethyl esters, particularly the ethyl levulinate, as reported inTable 4.

TABLE 4 Effect of Fenton's reagent (Fe(II) + H₂O₂) in the reactionmedium. Example number 13 14 15 16 [Fe(II)/H₂O₂] × 10⁻² [(g/g) 0.0/0.00.4/0.25 0.8/0.49 1.6/0.97 (mol ratio)](*) Product yield (wt %) EL 20.325.7 26.5 25.9 LA 1.5 1.6 1.8 1.6 EF 17.1 19.5 20.8 20.7 EA 5.1 6.1 7.56.4 2-F 0.3 0.5 0.0 0.3 Methanol 1.6 1.6 1.4 1.6 Total RP (sum of fiveabove lines) 45.9 55.0 58.0 56.5 DEE (by-product) 51.6 47.1 54.4 60.7(*)Ferrous sulphate heptahydrate (Anachemia). Concentration: Acid = 2.60wt %, H₂O₂ = 4.39 wt %.

Fe (II) ions present in quite small amounts produce hydroxyl radicalswith hydrogen peroxide that contribute to a more powerful and selectiveoxidizing cracking of the furfuraldehyde functions of the reactionintermediates in the cellulosic biomass conversion.

Ti (IV) ions in the presence of hydrogen peroxide is a powerfuloxidizing catalyst, Ti (IV) ions, in the form of Ti (IV)oxysulfate-sulphuric acid or Ti (IV) ethoxide, can be incorporated invery small amounts into the reaction medium that already contains themineral acid, hydrogen peroxide and ethanol. H₂MoO₄ andmethyltrioxorhenium (VII) can have similar effect.

Example 20 of Table 5, paragraph [0061] shows the positive effect of Ti(IV) on the yield of ethyl levulinate.

It is worth noting that hydrogen peroxide or the Fenton's reagent isused to degrade (very partially) the lignin component in thepre-treatment of ligno-cellulosic materials. This pre-treatment isnecessary for “opening” the wood or biomass structure, so that chemicalreactants or enzymes can reach the other components: hemi-cellulose andcellulose. This invention advantageously uses hydrogen peroxide,Fenton's reagent or hydrogen peroxide+TiO₂ also to selectively oxidizecellulose and hemi-cellulose: surprisingly, their degradation intocarboxylic acids much better occurs that results in very significantimprovement of the yields of the final products, i.e. ethyl esters(Tables 1 and 4).

De-Coupling of Reaction Networks

Polymerization of furfural and other aldehydic intermediates produced bythe conversion of ligno-cellulosic biomass generally accompanies theproduction of various liquid products, the commercially valuablecarboxylic acids (then rapidly convert into ethyl esters in the presenceof ethanol) and others. These polymers form with the unconverted ligninthe solid tars or lignin char (case of lignin containing biomass). It isusually very difficult to decrease the rate of formation of these solidtars.

Sodium sulphite and other inorganic or organic sulphites as well assodium and calcium carbonates are known to bind to the aldehyde functionof organic compounds. This invention can incorporate sodium sulphite(for instance) to the reaction medium, so that the rate ofpolymerization of various aldehydes intermediates or products can belowered (inhibition of polymerisation). Thus, per compensation effect,the yields of other conversion products can be increased. Tables 5 and 6report the results of such novel procedure: network 1=conversion toliquid products, network 2=polymerisation of aldehyde-basedintermediates to tars. Data of Table 5 show that, effectively, network 2is significantly depressed while network 1 is favoured, if sodiumsulphite is used as inhibitor of polymerisation.

TABLE 5 Inhibiting the polymerization of furfural and otheraldehyde-type reaction intermediates by incorporation of sodiumsulphite. Reaction conditions: 140° C. for 60 min and 157° C. for 240min; acid = 2.60 wt %, H₂O₂ = 3.57 wt %, [Fe(II)/H₂O₂] × 10⁻² (g/g/molratio) = 0.8/0.49. Example number 17 18 19 20* Na sulphite (wt %) 0.40.5 0.7 0.5 Acid concentration (wt %) 2.6 2.8 2.8 2.9 Product yield (wt%) EL 31.3 37.2 35.8 40.8 LA 2.7 4.5 5.4 4.1 EF 19.4 19.9 16.7 13.7 EA6.3 5.9 5.2 5.4 2-F 0.7 1.4 1.0 1.1 Methanol 1.6 1.5 1.5 3.2 Total RP(sum of five above lines) 62.0 70.4 65.6 68.2 DEE (by-product) 60.5 43.147.8 26.0 *Example 20: Use of Ti (IV) oxysulfate instead of Fe (II)sulphate with concentration of TiO₂ = ca. 0.03 wt %.

In order to decrease the production of DEE, quite low concentration ofacid is used (1.2 wt %) and some water is also added (ethanol/water wtratio=3.8). The other parameters are=raw material=dried spruce chips,H₂O₂=2.8 wt %, main catalyst: [Fe(II)/H₂O₂]×10⁻² (g/g/molratio)=0.8/0.49. The reaction temperatures are as follows: first heatingstep=195° C. for 12 minutes, and second heating step=172° C. for 35° C.

Table 6 shows that by using polymerization inhibitor (sodium sulphite,sodium carbonate-decahydrate, sulphurous acid ions, para-toluenesulfonic acid monohydrate (PTSA), calcium carbonate, by using very lowconcentration of acidic catalyst (sulphuric acid) and by adjusting thereaction temperatures and times, it is possible to significantlydecrease the formation of DEE while the yields of the main products arekept almost unchanged, except for the levulinic acid that significantlyincreases.

Example number 21 22 23 24 25 Polymerization inhibitor Na₂SO₃ Na₂CO₃H₂SO₃ PTSA CaCO₃ Product yields (wt %) EL 30.1 30.2 40.5 40.0 31.2 LA8.7 8.8 8.9 9.8 8.4 EF 17.6 17.3 21.2 17.6 18.1 EA 8.4 8.7 9.6 7.4 8.02-F 4.5 4.2 5.5 4.2 4.4 Methanol 1.0 2.1 1.7 1.4 1.2 Succinic acid 2.34.4 4.0 3.2 2.8 Total RP 72.6 75.7 91.4 83.6 74.1 (sum of five abovelines) DEE (by-product) 16.5 13.2 17.1 15.6 17.6

Close observation of these results shows that a small concentration ofH₂SO₃ or PTSA (<0.2 wt %) can significantly enhance the yield ofreaction products (RP) formed from the biomass itself (Ex. 23 and 24).

Conversion of (Unwanted By-Product) Diethyl Ether (DEE) intoCommercially Valuable Hydrocarbons

The present invention is illustrated in further details by the followingnon-limiting examples of the production of hydrocarbons from DEE, themain by-product of the conversion of biomass into ethyl esters. In fact,DEE and, optionally, light ethyl esters being produced by the acidethanolysis of biomass material, are sent over a zeolite acid catalyst,preferably ZSM-5 zeolite (acid form). The products of this catalyticreaction are hydrocarbons containing from 1 to 12 carbon atoms. Inparticular, liquid hydrocarbons having a number of carbon atoms rangingfrom 5 to 12 are those that normally correspond to petroleum gasoline.The presence of aromatics (BTX) enhance the octane rating of suchgasoline.

Experimental

Referring to FIG. 1, DEE (in some run, DEE and light ethyl esters) wasinjected by mean of an infusion pump into a vaporizer-vapour mixer (16).The resulting vapour was then sent into a tubular reactor (18) (quartztube, 50 cm long, 1.5 cm in outer diameter and 1.2 cm in innerdiameter). The temperatures were controlled and regulated by automaticdevices (not shown) that were connected to chromel-alumel thermocouples(set in the catalytic bed and in the pre-heating zone) and the heatingfurnace.

The testing conditions were as follows: temperature=280, 300 and 320°C.±2° C.; weight hourly space velocity (WHSV): 1.5-7.5 h⁻¹, weight ofcatalyst=1.0-2.0 g, run time=3 h. In some runs, water was added to thefeed, using another infusion pump being connected to the vaporizer-gasmixer.

A ZSM-5 based catalyst was used in the form of extrudates (H-ZSM-5,Si/Al=50, 20 wt % binder).

Liquid and gaseous products were collected separately, using a system ofcondensers. The gas-phase components were analyzed using a FID gaschromatograph that was equipped with a 30 m GS-capillary column (AgilentJ & W Scientific), while the analysis of the liquid phase was performedusing another FID gas chromatograph equipped with a HP-5 capillarycolumn (Agilent J & W Scientific, 30 m). The liquid phase was alsoanalyzed using a FID gas chromatograph equipped with a DB-Wax capillarycolumn (Agilent).

Catalytic Conversion of Diethyl Ether (DEE) into Hydrocarbons over ZSM-5Zeolite

Diethyl ether, by-product of this process, is then sent into a tubularreactor that is heated at 300° C. Reaction conditions are reported inTable 7. The conversion of DEE is almost complete. It is seen that thedilution of DEE by water is extremely beneficial because the cokedeposition dramatically decreases when steam is present, so that thezeolite catalyst can be used for quite long time without any need forregeneration (operation that consists of coke removal by combustion).The liquid hydrocarbons, having a boiling point ranging from C₅ to C₁₁,can be considered as gasoline-grade liquid, having a high octane-ratingbecause its relatively high content in BTX aromatics. The production ofmethane is almost nil: this is really an advantage because methane isnot a commercially very valuable product.

Not only the DEE can be used, but also a mixture containing DEE and somelow ethyl esters such as ethyl formate or ethyl acetate, can also beconverted into hydrocarbons. Finally, the separation of the products ofthis catalytic reaction (hydrocarbons-water) is an easy operation(simple decantation).

It should be noted that instead of using a tubular reactor working underatmospheric pressure, other reaction systems can be utilized that maygive higher yields of liquid products (ex: pressure tubular reactor).Other reactor shapes can also be used.

TABLE 7 Conversion of product diethyl ether (DEE) into hydrocarbons overZSM- 5 zeolite (Temperature = 300° C.; weight of catalyst = 2 g).Example number 26 27 28 29 WHSV (h⁻¹) 3.0 1.5 1.5 1.5 H₂O/DEE 0 0 0.51.0 weight ratio Total 97.7 98.4 98.2 98.2 conversion (wt %) Productyield (wt %): Liquid 53.3 (30.7) 54.7 (28.2) 56.2 (25.7) 54.5 (21.7)hydrocarbons (BTX aromatics) C₂-C₄ paraffins 37.0 40.0 34.7 26.8 Methane0.03 0.02 0.02 0.01 C₂-C₄ olefins 6.5 2.2 6.8 16.9(*) and diolefins Coke0.8 1.5 0.5 <0.1 (*)Ethylene = 6.2 wt %, Propylene = 4.8 wt %, butenesand butadienes = 5.9 wt %.

As reported in Table 7, at the temperature tested, the conversion of DEEis essentially complete. The yield in liquid hydrocarbons(gasoline-grade), even under atmospheric pressure, is much higher than50 wt %. Such gasoline has a high octane rating because its BTXaromatics content is relatively high. C₂-C₄ olefins and paraffins arecommercially valuable hydrocarbons owing to their uses in thepetrochemical industry (production of important plastics, syntheticfibers and rubbers).

It is worth noting that:

-   -   a) The yield of methane is low (<0.1 wt %);    -   b) The production of coke (main cause of catalyst fouling that        may result in quite rapid activity decay) is relatively low        (examples 26 and 27). Moreover, the addition of water (steam) to        the DEE feed (examples 28 and 29 versus example 27) does not        decrease the total conversion although some changes are observed        in the composition of products. The most surprising result is        that the coke deposition drastically decreases: this means that        the on-stream stability of the catalyst is considerably        improved, leading to improved economics for the process (less        catalyst regeneration operations needed) and also importantly,        much lower emission of greenhouse gases (carbon oxides);    -   c) Several catalysts have been tested, that include various        zeolites (H-Y, US-HY, acidic mordenite) as well as amorphous        acidic alumina. The preferred catalyst in terms of activity        (conversion) and high yields of gasoline (and light        hydrocarbons) is the H-ZSM-5. Even with the same zeolite        structure, the H-ZSM-5 (Si/Al=50) is most preferred over the        H-ZSM-5 (Si/Al=25) or the H-ZSM-5 (Si/Al=100). Still preferably,        modifying the ZSM-5 zeolite with Zn or Ga results in higher        product BTX (aromatics) yield.        Catalytic Conversion of Light Product Liquid into Hydrocarbons        over ZSM-5 Zeolite

As an option, the light products normally obtained in the firstconversion step (DEE along with other light ethyl esters and somemethanol, see examples 2 to 6) in ethanol solution, herein called lightfraction LF, were sent to the catalytic reactor that contained theH-ZSM5 (50). Table 8 shows that all these liquid products werecompletely converted into hydrocarbons.

TABLE 8 Conversion of liquid fraction F3 into hydrocarbons over ZSM-5zeolite catalyst Example number Light fraction (LF) 30 31 Reactiontemperature (° C.) 300 320 Water added (wt %) 0 20 Composition/yields(wt %) Diethyl ether (DEE) 38.9 trace Trace Ethyl formate (EF) 7.4 traceTrace Ethyl acetate (EA) 3.2 trace Trace Methanol (MeOH) 0.4 trace TraceEthanol (EtOH) 50.1 0.3 0.9 Methane 0 <0.1 <0.1 C₂-C₄ paraffins 0 24.839.4 C₂-C₄ olefins 0 26.5(*) 15.7(**) Gasoline-grade 0 (0) 46.6 (9.5)43.5 (7.7) hydrocarbons (BTX aromatics) Coke 0 1.8 0.4 (*)Ethylene =14.5 wt %, propylene = 4.8 wt %, butenes and butadienes = 7.2 wt %.(**)Ethylene = 7.4 wt %, propylene = 3.9 wt %, butenesand butadienes =4.4 wt %.

Various Combinations of Final Products

Following figure shows schematically the technology of the presentinvention: the conversion of ligno-cellulosic materials can result inone of the following spectra of final products.

-   -   1) Ethyl levulinate+gasoline+C₂-C₄ hydrocarbons+ethyl        acetate+ethyl formate+methanol, if only DEE is sent to the        second reactor.    -   2) Ethyl levulinate+gasoline (C₅-C₁₁ hydrocarbons)+C₂-C₄        hydrocarbons, if the light ethyl esters and methanol by-products        are sent together with DEE in the second reactor.

Particularly interesting is option 2) for the commercial uses of itsfinal products: diesel additive (ethyl levulinate), high octane ratinggasoline, C₂-C₄ olefins and paraffins as intermediates (forpolymers)/feedstocks for the petrochemical industry. In particular,C₂-C₄ paraffins (ethane and mostly propane and butanes) can be used asmotor fuel (liquefied petroleum gas, LPG).

As reported in the examples of Tables 5 and 6, in the best conditions ofthe main reaction (Examples 20 to 25), by using the various catalyticeffects combined in the reaction medium as mentioned earlier (oxidationby hydrogen peroxide/Fenton's reagent, and use of a polymerizationinhibitor) the liquefaction of the ligno-cellulosic biomass can reachthe level of 60 wt % of all the biomass used. A rough estimation showsthat, in the case of jack pine or spruce wood chips used as rawmaterial, almost all the cellulose component and up to 60-65 wt % ofhemicellulose component are converted in liquid products (the rest ofthe hemicellulose being transformed in solid polymeric species probablythrough the 2-furfural). The presence of methanol and that of some shortcarboxylic acids such as formic and acetic acids (both esterified byethanol), and also succinic acid, indicate that lignin is also convertedin such reaction conditions, however, to a much lower extent (15 to 20wt %). More lignin can be converted into liquid products if the reactionconditions are harsher (higher temperature, more oxidizer and longerdigestion time). This is a good approach for increasing the liquefactionlevel of ligno-cellulosic materials, over 60 wt % with spruce or pinewood chips herein investigated. However, these newly formed products area “mixture” of some water-soluble phenol derivatives that have probablylower commercial values.

The second step of the present invention that uses a ZSM-5 type zeolitecatalyst to convert diethyl ether (DEE) into hydrocarbons (gasoline andother gaseous hydrocarbons), as reported in Table 7. DEE can also act ashydrogen donor when it is fed with other compounds such as the lightesters as reported in Table 8. Preliminary testing of suchzeolite-catalyzed reaction using a mixture of DEE and these phenolicproducts shows that we can obtain a gasoline that is richer in aromaticsthan when DEE is used alone.

REFERENCES

-   (1) S. W. Fitzpatrick, U.S. Pat. No. 5,608,105 (Mar. 4, 1997).-   (2) R. Le Van Mao, Q. Zhao, G. Dima and D. Petraccone, Catal. Lett.    141 (2011) 271.-   (3) Q. Xiang, Y. Y. Lee, Appl. Biochem Biotech 84-86 (2000) 153.-   (4) M. Mascal, E. B. Nikitin, ChemSusChem 3 (2010) 1349.-   (5) J. H. Merz, W. A. Waters, J. Chem. Soc. S15 (1949).-   (6) R. Le Van Mao, L. Dufresne, U.S. Pat. No. 4,975,402 (Dec. 4,    1990).-   (7) R. Le Van Mao, J. Yao, U.S. Pat. No. 5,135,898 (Aug. 4, 1992).

1. A method for converting ligno-cellulosic biomass materials into ethyl esters and hydrocarbons, said method comprising the following steps: (a) the chemical-catalytic conversion of the biomass material into ethyl levulinate, light ethyl esters and other products including diethyl ether carried out with alcohol as reactant and solvent in dilute acidic medium and in the presence of an oxidizing agent, (b) the chemical-catalytic conversion of at least one of the diethyl ether light ethyl esters into hydrocarbons by reaction with an acid nanocatalyst and (c) the recovery of the resulting products.
 2. The method of claim 1 wherein the oxidizing agent is hydrogen peroxide.
 3. The method of claim 1 wherein the oxidizing agent is a Fenton-type reagent.
 4. The method of claim 1 wherein the oxidizing agent is hydrogen peroxide alone or hydrogen peroxide activated by at least one of Fe (II) ions or Ti (IV) ions.
 5. The method of claim 1, wherein the dilute acidic medium comprises an inhibitor of polymerization of aldehyde-type reaction intermediates.
 6. The method of claim 1 wherein the acidic nano-catalyst is a zeolite of ZSM-5 type.
 7. The method of claim 6 wherein the zeolite of ZSM-5 type has a Si/Al atom ratio ranging from 40 to
 60. 8. The method of claim 7 wherein the ZSM-5 zeolite is modified Zn or Ga.
 9. The method of claim 1, wherein the resulting products comprise ethyl levulinate (diesel-grade additive), light ethyl esters, methanol, gasoline-range hydrocarbons, C₂-C₄ hydrocarbons or mixtures thereof.
 10. The method of claim 5, wherein the inhibitor of polymerization of aldehyde-type reaction intermediates comprises sulfurous acid, para-toluene sulfonic acid, sodium sulfite, sodium carbonate, calcium carbonate, or any combination thereof.
 11. The method of claim 9, wherein the light ethyl esters are at least one of ethyl formate or ethyl acetate. 